PAKIS <;KKENS. 13 



METHODS OF ANALYSIS AND ANALYSES OF SAMPLES. 

 PARIS GREENS. 



In analyzing the samples of Paris Green the following determinations 

 were made: Moisture, sand, sodium sulphate, total arsenious oxid, 

 copper oxid, soluble arsenious oxid, and soluble copper oxid. The 



methods follow. 



% 



METHODS OF ANALYSIS AND DISCUSSION. 



Moisture. Diy 1 to 2 grams for eight to ten hours at 105 to 110 C., 

 and calculate loss as moisture. 



Sand. Dissolve the sample used for moisture determination in 

 hydrochloric acid, filter, wash, dry, and finally burn filter, calculating 

 the residue as sand. 



Sodium sulphate. Treat the boiling filtrate from the determination 

 of sand with a boiling solution of barium chlorid, allow to stand until 

 the precipitate settles, leaving a clear solution; filter, wash, dry. and 

 burn, with the usual precautions used in determining barium sulphate; 

 calculate the barium sulphate found to sodium sulphate, since it is in 

 this form that sulphuric acid is supposed to be present. 



Tottif in'iniiniN oxid. For this determination 11 standard iodin 

 solution is needed, which is prepared in the following manner: a 

 Dissolve 12.7 grams of powdered iodin in about 250 cc of water to 

 which has been added 18 to 25 grams of chemically pure potassium 

 iodid, and make the whole up to a volume of 1 liter. To standardize 

 this solution, weigh out 1 gram of dry, chemically pure arsenious oxid, 

 transfer to a 250 cc flask by means of about KM) cc of a solution con- 

 taining 2 grams of sodium hydrate in each 100 cc, and boil until all 

 arsenious oxid goes in solution; cool, make to a volume of 250 cc, and 

 use 50 cc for analysis. 



This f>o cc portion is concentrated by boiling in a 250 cc flask to 

 half its volume and allowed to cool to 80 C. An equal volume of 

 concentrated hydrochloric acid is now added, accompanied by 3 grains 

 of potassium iodid. mixed, and the whole allowed to stand for ten 

 minutes (to reduce the arsenic oxid formed on boiling an alkaline 

 arsenite to arsenious oxid). The brown solution is then diluted with 

 cold water, and an approximately N 10 solution of sodium thiosul- 

 phate added, drop by drop, until the solution becomes exactly color- 

 less. (This end-point is easy to read without the aid of starch.) This 

 solution is then made slightly alkaline with dry sodium carbonate 

 (using a drop of methyl orange to read the change), then made slightly 



See article by Hay wood, Jour, of the Amer. Chem. Soc., Vol. XXII, No. 9, 

 S>|,trniber, 1900. 



